Paris - Asian outbreaks of a notorious antibiotic-resistant super-germ are being driven by a gene that helps the bug colonise the nostrils, lungs and skin and evade the immune defences, scientists said on Sunday.
So-called methicillin-resistant Staphylococcus aureus (MRSA) is a major worry for hospitals because of its ability to hole up in wounds, tubes and surgical devices, infecting patients whose immune system is already weak.
MRSA outbreaks happen in waves as new strains of the bacterium take over from older configurations.
But how these epidemics become established is a process that genetically has until now been unclear.
Reporting in the journal Nature Medicine, researchers in the US and China say they found the key gene, sasX, in samples taken from 807 patients who had been treated for S aureus in three Chinese hospitals over the past 10 years.
Once extremely rare, sasX became more and more common, nearly doubling in frequency from 21% of samples in 2003 to 39% in 2011, they found.
At present, sasX is prominent in Asian strains of MRSA that have been detected, but it is likely to spread beyond the region, according to the report.
The gene is located in a so-called mobile genetic element, meaning that it is in a segment of DNA that can easily transfer from an old strain to a new one.
However, sasX "is a promising target" for drugs or vaccines, says the study, led by Michael Otto of the US National Institute of Allergy and Infectious Diseases (Niaid).